IEC 62271-109:2019 is applicable to AC series capacitor by-pass switches designed for outdoor installation and for operation at frequencies of 50 Hz and 60 Hz on systems having voltages above 52 kV. It is only applicable to by-pass switches for use in three-phase systems. This document is also applicable to the operating devices of by-pass switches and to their auxiliary equipment. This third edition cancels and replaces the second edition published in 2008 and Amendment 1:2013. This edition constitutes a technical revision. This edition contains the following significant technical changes with respect to the previous edition:a) the document has been restructured according to edition 2.0 of IEC 62271-1;b) the rated voltage assignation across the by-pass switch has been aligned to the rule defined in IEC 60143-1;c) clarification has been given regarding rated continuous current of compensated and uncompensated line;d) some clarifications have been given following a loss of "suitable precautions";e) as per Amendment 2 of IEC 62271-100, the section "Rated time quantities" has been moved to Clause 6 under "Time quantities";f) as per Amendment 2 of IEC 62271-100, the section "Test for static mechanical loads" have been moved to Clause 6 under "Static mechanical loads";g) additional rules have been introduced for vacuum interrupters during impulse tests;h) additional clarifications have been given regarding the number of reduced impulses during impulse tests;i) a wider tolerance on the current damping during by-pass making current test-duty has been introduced.